This invention relates to vacuum bottles with a bellows pump, so called "Air Pots". More particularly it relates to an improvement in a vacuum bottle with a manually operated bellows pump which serves to pump air into an interior of an inner bottle to increase the internal pressure in the inner bottle, thereby pouring the liquid in the inner bottle therefrom through a pumping tube and a pouring tube without lifting the vacuum bottle.
In the conventional vacuum bottles of the kind mentioned above, there has generally been employed a bellows pump comprising a bellows body, upper and lower plates formed separately from the bellows body and fused to the openings of the bellows body, and a return spring placed between the upper and lower plates to keep the bellows body expanded. Although such a bellows pump has a simple construction, it is difficult to join the bellows body to the upper and lower plates by fusing because the bellows body is molded with polyethylene which possesses good extensibility but poor fusing characteristics. Thus, it takes a great deal of skilled labor forces in its assembly operation. In order to overcome such a problem, it has been proposed to use an integrally molded bellows pump of which the upper and lower plates are molded as integral parts of the bellows body with polyethylene. In such a bellows pump, the lower plate is provided, at its central portion as an integral part therof, with a downwardly projecting small air tube which is screwed or pressed into an opening provided in the bottom of a lid body. Because of the poor creep characteristics and softening of polyethylene, however, there is a fear of air leakage resulting from the decrease of the fitting force between the bellows pump and the lid body during long service. In addition, it is troublesome to introduse the return spring into the bellows pump since the spring must be inserted through the small air tube or air inlet.